The invention relates to a chip carrier for microwave semiconductor components.
For microwave semiconductor components, for example integrated gallium-arsenide microwave circuit chips, it is necessary to provide characteristic impedance-correct package assemblies. In the encapsulation of microwave semiconductor chips in a housing or in the seating of microwave semiconductor chips on a chip carrier, such package assemblies should exhibit optimum microwave properties, good heat dissipation, full testability and easy installability by the customer.
If a semiconductor chip is mounted directly in a circuit without the use of a chip carrier, this semiconductor chip can be tested only to a limited extent before it is mounted. This results in a relatively high failure rate for such a semiconductor chip.
The U.S. Pat. No. 4,115,837 discloses a chip carrier for an integrated circuit wherein the integrated circuit is placed on a substrate of insulating material. To be able to accommodate a maximum number of electrical connections with the integrated circuit, the insulating substrate extends outward beyond a support in that area in which it is to be secured on the support. For microwave applications such a support is not provided. For testing purposes, a metallization is applied on the outer edge of the underside of the insulating substrate. This less than full-area metallization interferes with the transmission of microwaves. In order to be able to carry out a test, this chip carrier has an electrical connection of complicated design between the chip and this metallization on the underside of the insulating substrate. Except for testing purposes, the grounding lead of the chip does not extend through the underside of the insulating substrate.
The U.S. Pat. No. 4,340,902 discloses a chip carrier in which the chip is placed on a metal element for better heat removal. Via a complicated grounding lead, which traverses a multi-layer ceramic structure, the chip is connected with a metallic plate that is disposed between the foundation of the chip and the support. The construction of this chip carrier is complicated and not adaptable in a versatile manner to all types of microwave components on all types of boards.
The U.S. Pat. No. 3,864,727 discloses a chip carrier in which the chip is placed on an insulating substrate. This insulating substrate, in turn, is applied on a metallic support which, in the area on which the substrate is applied, extends substantially beyond the substrate. Such a chip carrier has wide strip lines, cannot be placed on circuit boards, and is not suitable in its construction for microwave circuits.
The U.S. Pat. No. 3,946,428 discloses a chip carrier in which, in a recess of a dielectric substrate, the chip is placed on a metallic intermediate element which, in turn, is placed on the metallic support. Here the metallic support has the same external dimensions as the dielectric substrate. A characteristic impedance matching is effected through the provision of additional dielectric elements. This complicates the construction, which permits only a small number of strip lines.
The U.S. Pat. No. 3,769,560 discloses a chip carrier which has a complicated design and requires special electrical connections for electrical grounding lines. Such a chip carrier is not particularly suitable for microwave applications.
The U.S. Pat. No. 3,590,341 discloses a chip carrier which, for the installation of a transistor, requires, for reasons of symmetry, two electrical leads to the emitter of the transistor. These separate leads to the emitter need considerable space not only on the chip carrier, but also on the circuit board on which the chip carrier is to be placed. Furthermore, these leads are expensive due to the material they require. This particular chip carrier also exhibits poor heat dissipation.
The U.S. Pat. No. 3,651,434 discloses a chip carrier in which a dielectric substrate is placed on a support. Inside a recess in the dielectric substrate, a microwave component is placed on the support. Between the dielectric substrate and the support at least one area is provided in which the support is coated with a metallization. This metallization extends from the area in which the dielectric substrate rests on the support, far beyond the dimensions of the dielectric substrate. The dielectric substrate is relatively thick. Therefore the electric connections must be relatively thick over their entire length, thereby permitting only a low packing density of electrical leads. Not only is the construction of such a chip carrier complicated, but it also is not particularly favorable for microwave applications. In particular it is not possible, or at least not in a simple manner, to adapt such a chip carrier with its electrical connections to various purposes of use; that is, to various user circuits.